Hey New2net98~Good question.

If someone has sufficient enzymes to break down dietary proteins, then although I don't think it is a good idea to do, they should be able to break down the amino acids of which dietary proteins are comprised.

This would be very comparable I think to someone with sufficient protease being able to digest gluten. They could most likely ingest the peptides, of which gluten is comprised, without a toxic reaction. Someone that has lost the ability to digest gluten (due to a lack of protease) would most likely have a toxic reaction to the peptides.

The difference is you are talking about athletes and bodybuilders etc. verses autoimmune sufferers. I am not saying ingesting amino acids for a healthy individual will give you autoimmune disease, just that if you have lost these enzymes and are having symptoms of autoimmune disease, ingesting isolated components of these proteins will most likely,as the lupus study showed, increase your disease risk.